Unmanned aircrafts have already droned through the sky and pilotless automobiles be able to work on the way have been in test, while the hoistman on a mobile crane can't judge whether a lifting block is vertical during lifting, hence the hoistman is controlled by a hoisting commander based on the information provided by a monitor keeping watch on loads lifted vertically, which isn't in time and accurate.
According to 9.1.4 in Technical Standards for Construction of Large Equipment Hoisting Engineering, the crane hoisting technology should comply with a standard that the deviation angle of the lifting hook should be less than 3° during lifting. According to 12.2.13 in Specification for Hoisting Construction of Petrochemical Engineering, the deviation angle of the lifting hook shouldn't exceed 3° during lifting loads using mobile cranes. The deviation angle can't be detected accurately, because cranes must lift loads with lifting blocks rather than there aren't detecting instruments. Therefor, the key problem is how to detect the deviation angle of the lifting hook on the lifting blocks accurately.